package object

import (
	"fmt"
	"os"
)

var Builtins = []struct {
	Name    string
	Builtin *Builtin
}{
	{
		"len", &Builtin{
			Fn: func(args ...Object) Object {
				if len(args) != 1 {
					return newError("wrong number of arguments. got=%d, want=1", len(args))
				}
				switch arg := args[0].(type) {
				case *Array:
					return &Integer{Value: int64(len(arg.Elements))}
				case *String:
					return &Integer{Value: int64(len(arg.Value))}
				default:
					return newError("argument to `len` not supported, got %s", args[0].Type())
				}
			},
		},
	},
	{
		"puts", &Builtin{Fn: func(args ...Object) Object {
			for _, arg := range args {
				fmt.Println(arg.Inspect())
			}
			return nil
		},
		},
	},
	{"first",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1",
					len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `first` must be ARRAY, got %s", args[0].Type())
			}

			arr := args[0].(*Array)
			if len(arr.Elements) > 0 {
				return arr.Elements[0]
			}
			return nil
		},
		},
	},
	{
		"last",
		&Builtin{Fn: func(args ...Object) Object {
			if len(args) != 1 {
				return newError("wrong number of arguments. got=%d, want=1", len(args))
			}
			if args[0].Type() != ARRAY_OBJ {
				return newError("argument to `last` must be ARRAY, got %s", args[0].Type())
			}
			arr := args[0].(*Array)
			length := len(arr.Elements)
			if length > 0 {
				return arr.Elements[length-1]
			}
			return nil
		},
		},
	},
	{"rest",
		&Builtin{
			Fn: func(args ...Object) Object {
				if len(args) != 1 {
					return newError("wrong number of arguments. got=%d, want=1", len(args))
				}
				if args[0].Type() != ARRAY_OBJ {
					return newError("argument to `rest` must be ARRAY, got %s",
						args[0].Type())
				}
				arr := args[0].(*Array)
				length := len(arr.Elements)
				if length > 0 {
					newElements := make([]Object, length-1, length-1)
					copy(newElements, arr.Elements[1:length])
					return &Array{Elements: newElements}
				}
				return nil
			},
		},
	},
	{"push",
		&Builtin{
			Fn: func(args ...Object) Object {
				if len(args) != 2 {
					return newError("wrong number of arguments. got=%d, want=2", len(args))
				}
				if args[0].Type() != ARRAY_OBJ {
					return newError("argument to `push` must be ARRAY, got %s",
						args[0].Type())
				}
				arr := args[0].(*Array)
				length := len(arr.Elements)
				newElements := make([]Object, length+1, length+1)
				copy(newElements, arr.Elements)
				newElements[length] = args[1]
				return &Array{Elements: newElements}
			},
		},
	},
	{
		"exit", &Builtin{
			Fn: func(args ...Object) Object {
				if len(args) > 1 {
					return newError("wrong number of arguments. got=%d, want=1", len(args))
				}
				if len(args) == 0 { // 无参数 默认以exit(0)执行
					os.Exit(0)
				}
				if args[0].Type() != INTEGER_OBJ {
					return newError("exit code must be int, got %s", args[0].Type())
				}
				os.Exit(int(args[0].(*Integer).Value))
				return nil // 不会被执行到
			},
		},
	},
}

func newError(format string, a ...interface{}) *Error {
	return &Error{Message: fmt.Sprintf(format, a...)}
}

func GetBuiltinByName(name string) *Builtin {
	for _, def := range Builtins {
		if def.Name == name {
			return def.Builtin
		}
	}
	return nil
}
